How to clean up mesh after using Knife Project on a curved surface
try to make a strait line as on the pictur it shuld atleast look better.


if you whant to kep the shape add a new edge close to it and work whith it insted.


the last thing I whant to say is if you combinde the subsurfes and mirror modefiers. Put the mirror modefier firs if you don't whant a sharp edge on the mirror point.